> For the complete documentation index, see [llms.txt](https://overleaf-pro.ayaka.space/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://overleaf-pro.ayaka.space/latex/zh-tw/lei-bie-dang/01-understanding-packages-and-class-files.md).

# 了解套件與類別檔

LaTeX 文件中的預設格式設定由 **類別** 所使用的類別決定。這種預設外觀可以透過 **套件**。類別檔案名稱具有 **.cls** 副檔名，套件檔案名稱具有 **.sty** 副檔名。

## 類別與套件之間的差異

有時候在決定要撰寫套件還是類別時很難做出選擇。基本原則是：如果你的檔案包含控制某種特殊文件類型之邏輯結構外觀的命令，那麼它就是類別。否則，如果你的檔案增加的是與文件類型無關的功能，也就是說可用於書籍、報告、文章等等；那麼它就是套件。

例如，如果某公司需要帶有品牌識別的報告，使用特殊字型並且在頁尾放置公司標誌；你就需要一個新的類別。

如果該公司需要一個新命令，讓你更容易在文件中強調重要句子，在這種情況下，新的套件就能派上用場。

## 延伸閱讀

更多資訊請參見

* [撰寫你自己的套件](/latex/zh-tw/lei-bie-dang/03-writing-your-own-package.md)
* [撰寫你自己的類別](/latex/zh-tw/lei-bie-dang/04-writing-your-own-class.md)
* [供類別與套件作者使用的 LaTeX2ε](http://www.latex-project.org/guides/clsguide.pdf)


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